The present invention relates to an apparatus for controlling the fuel injection advance angle of a fuel injection pump.
In order to electronically control the timing of the supply of fuel to an internal combustion engine in accordance with the condition of the operation of the internal combustion engine, there have been proposed various kinds of apparatuses for controlling fuel injection advance angle. In one widely used conventional apparatus for controlling fuel injection advance angle there is employed a hydraulic type timer composed of a timer piston and a solenoid valve. In this apparatus, the solenoid valve is continuously closed/opened in response to a pulse signal so as to regulate the hydraulic pressure applied to the timer piston. Changes in the duty cycle of the pulse signal cause changes in the average opening degree of the solenoid valve, whereby the position of a member for adjusting the fuel injection advance angle of a fuel injection pump, which is connected with the timer piston, is controlled. Such an apparatus is disclosed, for example, in Japanese Patent Application Publication Nos. Sho 56-52530 and Sho 58-74836.
However, since the solenoid valve is always kept in a state of being repeatedly closed/opened by the application of the pulse signal at a frequency of some 10 Hz in this conventional apparatus, there are disadvantages that the service life of the solenoid valve is short and the reliability of the operation is low. Furthermore, when an expensive solenoid valve with excellent durability is employed in order to obtain a long service life and to increase the reliability of the device, it is disadvantageous in that the manufacturing cost increases.